Method of melting finely divided metal



Aug. 10, 1937. o. GARWIN METHOD OF MELTING FINELY DIVIDED METAL 2 Sheets-Sheet 1 Original Filed Oct. 18, 1932 I 6 4 0 9 4 3 4 o 6 u! /1 3 3 1 2 Y Y 8 7W 4 3 M Ola h lm l M r W k M" .H z a. 2 H1 Wm u h. lllll z l m 00 .9, M 7 3 5 3. s 5 \Q 2 i Pu, F I 9,,

I ml haw MW 3% M@ m & a @bw m Y Patented Aug. 10, 1937 UNITED STATES PATENT OFFICE Louis 0. Garwin, Cleveland Heights, Ohio Application October 18, 1932, Serial No. 638,291 Renewed March 2, 1937 3 Claims.

The present invention, relating as indicated to a method of and apparatus for melting finely divided metal, is more particularly directed to a method and apparatus for melting finely divided 5 aluminum scrap in even such finely divided form as borings, turnings, grindings and the like, converting this finely divided scrap material into pure metal or metal alloy and placing it in such condition that clean, sound castings may be made directly therefrom without employing any additional steps such as have heretofore been found necessary after the molten metal has been drawn off from the melting furnace.

To the accomplishment of the foregoing and related ends, said invention, then, consists of the means and steps hereinafter fully described and particularly pointed out in the claims; the annexed drawings and the following description setting forth in detail certain means and one mode of carrying out the invention, such disclosed means and mode illustrating, however, but one of the various ways in which the principle of the invention may be used.

In said annexed drawings:

Fig. l is a central vertical section more or less diagrammatic in character of one form of my improved apparatus; Fig. 2 is a transverse section on the line 22 in Fig. 1; Fig. 3 is a horizontal section .on the line 33 in Fig. 1; Fig. 4

is an end elevation of one of the end plates for the mold assembly shown in Fig. 2; Fig. 5 is a side elevation of the same; Fig. 6 is a plan view of one of the mold sections; and Fig. '1 is an end elevation of the same.

The melting of aluminum, aluminum alloys and analogous metals or metallic alloys presents certain problems which are not present in the 'handling of metals such as iron', brass and the like, in that these metals, which will hereinafter 40 be referred to generally as aluminum, almost instantly oxidize and become coated with aluminum oxides when heated and exposed to the air. As a result of this characteristic it has been possible to remelt and use finely divided scrap aluminum only with considerable difliculty and under certain carefully maintained conditions.

. Even under these circumstances it has been found impossible to thoroughly clean the metal in the remelting furnace and additional operations have been carried out upon the metal following its withdrawal from the furnace in an attempt to more nearly approach the desired quality of the reworked material.

' The equipment in use up to the present time for the remelting of finely divided aluminum has possessed certain objectionable features and tie furnaces with which I am familiar have required the use of a bath of molten material of unnecessarily large size, involving undue oxidation losses, increased labor costs and leaving the 5 furnace available for less production time; and have produced harmful effects on the metal being melted by reason of permitting it to be in contact with the atmosphere at elevated temperatures or with fuel gases; and by having 10 corners in which dresses collected to form nuclei for chemical and physical contamination; and by lacking proper means to adequately clean the molten metal by mechanical rupture of its inclusions therefrom; and by reason of the shape of the furnace chamber have allowed freezing" of the contents at times and have made it extremely difilcult to remove iron particles which invariably find their way into the bath and contaminate the aluminum. In addition to these 20 objections the ordinary furnaces have, by reason of their shape, been uniformly subject to distortion in operation, and while this objection does not afiect the operation of the furnace it has seriously affected the life of the furnace lining 25 and the maintenance cost of the equipment.

The present invention is directed to a method and apparatus which avoid the difliculties heretofore met with, render it possible to rapidly and uniformly remelt and clean finely divided 30 aluminum material in the furnace and withdraw completely purified, sound metal capable of being formed into desired cast'shapes. Briefly stated, y, improved method consists in charging into a furnace chamber containing a bath of 35 .clean, molten aluminum, additional finely divided aluminum, immersing the additional material in the bath, melting this material by heat conducted from a second chamber communicating with the first and also containing molten 40 aluminum, and cleaning the said material from dirt, gases and other foreign material while maintaining an inert atmosphere over that portion of the furnace into which the additional finely divided material is charged to prevent oxi- 45 dation, loss and inefliciency in the operation of the furnace. My method will be more clearly understood from reference to the furnace shown nace l consisting of an outer retaining sheet 2 of metal and an inner refractory lining 3 which 55 may conveniently be formed of plastic refractory material formed or plastered against the outer retaining shell of a sufllcient depth to providea lining of suitable characteristics for the melting of such materials as aluminum and other light metals to which the present process is adapted. The furnace is formed with 'a slightly inclined bottom or floor i which is common to the two chambers 5 and 6 of the furnace, which in turn are formed by a partition wall 9 extending downwardly from the arched roof portions 7 and 8 disposed above the two chambers of the furnace, the partition extending to a point which is sufficiently spaced from the floor 3 to allow of free passage of metal from one portion of the chamber to the other and also to permit of a rapid and free interchange of heat from the material in the chamber 5 to the material in the chamber 6. As an aid to the passage of heat from one said chamber to the other the partition 9 may be formed of a refractory material of relatively high conductivity.

The chamber 5 of the furnace serves as a chamber in which heat is applied to melt the metal and to maintain metal in molten condition and is provided with a curved inner wall ill (see Fig. 3) to reduce to a minimum the loss of material through the formation of oxides or the lodging of dross or foreign material in corners, which has been an objectionable feature in many furnaces of this type. This chamber 5 is provided with an opening in its outer wall above the level of the bath to be maintained therein, which is normally closed by means of a door I2 connected with a counterweight I3 for convenient operation. It is also provided with a fuel inlet port i4, through ,which any suitable fuel, such as oil, gas or other material may be introduced into the upper portion I5 of the chamber where the burning fuel will supply heat directly to the surface of the molten bath of material in the chamber. A small passage I5 extends through the partition wall 9 and allows products of combustion to flow intothe upper portion I1 of the chamber 6. -The products of combustion of the fuel burned in the space I5 will discharge by leakage around or past the door I2 and only a small amount of gas will pass through the passage I6 into the chamber I].

The second chamber 5 is similar to the first chamber in general form, but is provided with an outer wall I8 of considerable slope to permit of convenient removal of chunks of iron or foreign material which may accidentally be charged into 4 this chamber and which may then be removed by raking or by electro-magnetic means, the inclined wall I8 serving as a slope against which such material may be removed. At the top of the inclined wail I8 is a door 20 connected to a suitable counterweight 2I for convenient operation, this door normally closing an opening in the wall of the furnace, through which access may be had when necessary to the interior of the furnace chamber. The upper or dome-like roof of the chamber 6 is provided with a vent or stack aosa'ma is supplied, and from this hopper the material flows down onto the inner wall or ledge 30 of the passageway 23, where it is preheated to. a point slightly below its melting point by the. temperature of the atmosphere which is maintained on top of the bath in the chamber 6. The charge ordinarily carried on this ledge 30 is then forced off from the ledge and allowed to drop into the molten bath whenever desired by operating the charging piston 26 by means of a crank 21. At all times, however, this exit from the chamber H is sealed either by the charging piston 26, when in the position shown in Fig. 2, or by the material resting on the'ledge or bottom of the passageway 23 when the piston is retracted.

Agitating means for the purpose presently to be described are provided in the form of a shaft 35, slidably and rotatably mounted in a bracket or carrier 36, which in turn is supported by means of a fluid pressure cylinder 31 from a trolley 38 which is movable horizontally along a trackway 39. Movement of the trolley 38 and agitating means carried thereby in a direct on along the trackway away from the furnace will cause actuation of a switch 80, opening the cirand roughly fitting into a suitable opening 49 in cuit of the motor 40 and causing'cessation of the operation of the agitating mechanism. A return of the trolley and other parts to the position shown in Fig. 1 will also automatically close the switch and reestablish the circuit. Also carried on the bracket 36 is a motor 40 provided with a worm M driving a worm gear 42 which is slidably but non-rotatably mounted on the shaft 35 so'that rotation of the motor 4d causes rotation at predetermined speeds of the shaft 35. On the lower end of the shaft is mounted an agitating mechanism having a series of irregularly arranged andspaced arms 45, which are preferably of different lengths for reasons to be presently described. At the upper end the shaft is provided with a free handle 46 for convenient manipulation, while intermediate its ends it may be provided with a more or less spherical enlargement 4'! formed of suitable refractory material the door 20 to permit of manipulation of the agitating means in the chamber by operation of the handle outside of the chamber.

At the base of the furnace, pouring spouts 5n and 5| are provided (see Fig. 2) for pouring the molten material when desired, either into ladles or directly into the molds, the openings being normally closed by plugs of refractory material in the usual manner. Also at the lower point of the fioor of the furnace there is an eration by charging pieces of aluminum into the.

furnace, melting these to produce a bath of material sufiicient to rise above the top of the opening connecting the two chambers 5 and 5, above the bottom of the partition 9. Thereafter finely divided material may be charged into the furnace by the charging piston 24 in suificient quantities and at sufiicient intervals to compensate for molten material which is withdrawn as required for casting into ingots or other articles. The heat for melting the initial charge, and also the continuing charges, is supplied through the fuel inlet I4 and the fuel burns in the space I5 above the chamber 5. A small amount of burning fuel passes through the port I6 into the space I! above the chamber 6 and the burning of this fuel in the space I! burns out the oxygen in this space, leaving an inert, non-oxidizing atmosphere above the bath in the chamber 6. Additional products of combustion leak from the space l5 to the space I! and any excess gas in the latter space is allowed to discharge through the vent 2|.

The material in the chamber 6 is heated by conduction through thepartition wall 9 and also 10 by conduction through the metal connecting the bathsin the two chambers 5 and 6 and possibly, to some extent by some type of thermo-siphonic circulation through the molten material.

After the furnace has been placed in operation and a bath of appreciable depth secured, further operation of the apparatus and of the process is asfollows. A charge of finely divided aluminum is first allowed to pass from the hopper on to the ledge 30, "where'it is preheated by the gaseous contents of the chamber I! to a temperature which appro the heat-treating temperature of aluminum, which is a temperature which approaches but does not reach the melting temperature of the material. This nearly molten charge is then pushed from the ledge into the bath by the piston 24. The finely divided material falls upon the surface of the bath, passing throughany coating of dross thereon, and is gradually absorbed into the bath by melting, this absorption being relatively rapid because of the elevated temperature of the newly charged material. During this part of the operation the agitating means may be rotated either very slowly or not at all until the charged solid material has become molten and is mixed with the bath, and it is desirable to have a minimum of agitation at this stage as otherwise too thick a layer of dross is formed on top of the bath, which tends to hinder entrance of the new material into the bath proper. After absorption into the bath, however, of the new charge the agitation is increased in speed as rapidly as possible until a blade speed is secured of approximately 700. feet per minute. It will be understood thatsuitable fluxes, the 4 nature of which should be dependent upon the analysis of the materials employed, are included in the bath being charged with the aluminum or separately as may be found most suitable. Also the material charged into the bath should preferably be partially cleanedbefore charging to remove as much as possible of the dirt, oil and grease which is ordinarily inseparable from fine material of the type referred to. A certain amount of such material, however, will inevitably be included with the charge and will be agitated and burned upon the surface and above the surface of the bath. -The burning of thismaterial will occupy but a short time and will 60 leave the upper portion ll; of the chamber 6 with a non-oxidizing'or inertatmosphere in contact with the surface of the bath and with the material'waitingrto-be charged upon the ledge beneath the hopper. By thusjremoving the ac- 65 tive combustion and heating from that portion of the furnace in which material is charged I avoid the very rapid oxidation of such material and the consequent loss of material and increased time and eifort required to clean it which isin- 70 evitable in the types of remelting furnaces heretofore used.

From the foregoing description it will be evident that my method of melting finely divided aluminum consists in maintaining two connectingbaths 75 of the material, charging pre-heated solid mate'- rial into one of the baths while transmitting heat from the other of the said baths through the intervening partition and the intervening mass of metal into the bath into which the newly charged material is received. The apparatus described is constructed to facilitate the eifective carrying out of this method. The chamber 5 is formed of roughly frusto-conical shape, affording a large surface to the bath, to which heat is imparted from the upper portion of the chamber. In this way a maximum amount of heat can be transmitted into the bath and then transmitted through the bath to the connecting neck ofmetal lying beneath the partition wall 9. By constructing a partition wall of relatively conductive material alarge amount of heat can also be transmitted directly through this wall. At the same time the atmosphere above the bath in which the finely divided material is being preheated and subsequently absorbed into the bath is maintained in an inert condition, thus preventing the rapid oxidation of this material, which has been a difiiculty in most types of furnaces for the remelting of fine material.

The agitation given to the material is of prime importance. During the stage when new material is charged into the bath in chamber 6, or when this newly charged material is being melted and absorbed into the bath the latter should be agitated as little as possible, as otherwise the full absorption of the newly charged material is prevented. As soon, however, as the bath in the chamber 6 is fully molten the agitating means are operated vigorously and rapidly, being directed throughout the bath by the attendant who controls the operation from outside of the furnace, making it possible to operate upon every portion of the bath in an irregular and unrhythmic manner which does not set up continuous rhythmic streams of material, but breaks and tears apart the material throughout the bath by churning, striking and violently agitating all of this molten material. The agitation of the material in this manner in conjunction with the flux has a result of reducing the surface tension of the mass, loosening what may be termed the bond between the particles of clean metal and unclean metal, permitting the entrained and cocluded gases to be freed from the material. This action is continuous and relatively uniform through the entire bath where the action of the irregularly operated agitating means ruptures the surface skin tension of the material at every point, and the agitating arms then literally break loose the foreign matter from the pure metal, causing the foreign material to rise to the surface of the liquid in the form of dross. By maintaining a very rapid, violent, but irregular action of the agitating means I have found it possible to free molten metal entirely of its foreign material accumulation becomes excessive and interferes with the passage of finely divided charge into the bath proper, but until it becomes excessive this layer of dross acts as a protective coating, sealing the bath from even the inert atmosphere above it and insuring against oxidation of the molten 4- aosa'ma of the folldwifig claims or the equivalent of such metal by any stray currents of oxidizing gas which may drift into the upper portion of the chamber 6 from the heating chamber i5.

The material thus purified can be drawn ofl at intervals through the spouts 50 and bi into suitable molds to form either ingots or cast articles of any desired shape, and, treated as above described, the metal thus drawn off is relatively pure and of high enough quality to make it unnecessary to include any subsequent cleaning operation, as is invariably the case with furnaces now in use in which the metal is drawn ofi into ladles, which are then agitated by attendants with rakes to complete the removal of the foreign material. For production of ingots I have devised molds, which are shown in Fig. 2, and which will now be described. A

My improved molds consist of horizontal elements 60 (see Fig. 2) provided with recesses 6i separated from each other by full height partitions 62 and by low partitions 63 which permit the two ingots formed in each of the two partially formed chambers to be connected but still capable of being broken apart either upon cooling or with very little effort by the user. The chambers 6! are fed by sprues 64 at the'ends, which connect with sprue .65 branching from a main pouring sprue 66 which is formed in the, end plate 61 of the mold assembly, shown in Fig. 2. In assembling the molds a base 68 is first employed, after which a series of molds 60 are mounted in regi istration with each other upon the base, and the end plates 61 are applied and clamped in position by means of straps 69 extending around the side of the mold box from one end plate to the other, where they are tightened by means of cams l and handles H.

By forming the molds in this manner and grinding to a true surface all of the contacting 4o surfaces of the base, mold and end plates it is 45 the ingots from each other and to provide a mold of long life which is easily assembled and disassembled.

Other forms may be employed embodying the features of my invention instead of the one here- 50in explained, change being made in the formor construction, provided the elements stated by any stated elements be employed, whether produced by my preferred method or by others embodying steps equivalent to those stated in the following claims.

I therefore particularly point out and distinctly claim as my invention:-

1. In a method of melting finely divided aluminum, the steps which consist in maintaining two connected baths of molten aluminum, heating one of said baths, transmitting a portion of the heat imparted to the first-named bath to the other of said baths, maintaining a substantially inert atmosphere in contact with the second of said baths, charging into the last named bath a quantity of pre-healted aluminum, slowly agitating said bath during absorption of such charge thereinto, and then violently agitating said bath to clean the molten aluminum therein and to cause the separation of all foreign material from the aluminum. 1

2, In a method of melting finely divided aluminum, the steps which consist in maintaining two connected baths of molten aluminum, imparting heat to one of said baths, conducting part ofthe heat imparted to said bath to the other of said two baths, maintaining a substantially inert atmosphere in contact with the second of said baths, preheating a charge of finely divided alubath to a temperature slightly below the melting point, charging such preheated aluminum into said second bath, slowly agitating said bath until the said charge is absorbed thereinto in molten condition, and then agitating said bath violently to separate foreign material from the aluminum.

3. In a method of melting finely divided aluminum, the steps which consist in maintaining two connected baths of molten aluminum, heating one of said baths by means of fuel burned above said bath, transmitting a portion of the heat imparted to said first-named bath to the other of' said baths, transmitting a portion of said burning fuel to the space above said second bath so as to maintain a substantially non-oxidizing atmosphere in contact with said second bath, and violently agitating said last-named bath to clean the molten aluminum'therein and to cause the separation of all foreign material from the aluminum.

LOUIS O. GARWIN.

minum in such inert atmosphere over said second- 

